1. Field of the Invention
The present invention relates generally to a method and apparatus for receiving control information in a mobile communication system, and in particular, to a method and apparatus for receiving a control channel in an Orthogonal Frequency Division Multiplexing (OFDM) mobile communication system.
2. Description of the Related Art
OFDM, a scheme for transmitting data using multiple carriers, is a kind of Multi-Carrier Modulation (MCM) that converts a serial input symbol stream into parallel streams and modulates each of the streams with a plurality of orthogonal sub-carriers, i.e., sub-carrier channels, before transmission. Further, OFDM is actively being researched and applied in wireless communication systems.
FIG. 1 is a diagram illustrating an example of resource allocation in time and frequency domains in a conventional OFDM-based mobile communication system. In a conventional OFDM system, one modulation symbol (e.g., Quadrature Phase Shift Keying (QPSK) or 16-ary Quadrature Amplitude Modulation (16QAM)) is normally transmitted over one sub-carrier. Therefore, the sub-carriers are commonly considered as basic resources.
Referring to FIG. 1, the vertical axis 105 represents a time axis (or a time domain), and the horizontal axis 104 represents a frequency axis (or a frequency domain). Reference numeral 101 represents one sub-carrier, and reference numeral 102 presents one OFDM symbol. As illustrated in FIG. 1, one OFDM symbol is commonly composed of a plurality of sub-carriers. In addition, the common OFDM system unites a plurality of OFDM symbols into a basic transmission unit.
The basic transmission unit composed of several OFDM symbols will be referred to herein as a ‘Transmission Time Interval (TTI)’. Therefore, as illustrated in FIG. 1, one TTI 107 is composed of a plurality of OFDM symbols. Further, a smallest unit 103 shown in FIG. 1 will be referred to as a ‘Resource Element (RE)’. Thus, one TTI 107 includes a plurality of REs. In FIG. 1, one slot 106 is a basic unit constituting a physical channel, and RB 108 is a resource block, which is a basic unit in the frequency domain, constituting a data channel.
A Shared Control Channel (SCCH) is a channel that contains frequency resource information necessary for transmitting and receiving a Shared Data Channel (SDCH), Modulation and Coding Scheme (MCS) information, and Hybrid Automatic Repeat reQuest (HARQ) information. In the downlink, a terminal or User Equipment (UE) receives an SCCH to determine which frequency resources are used by an SDCH and in which format the SDCH is transmitted, in order to normally demodulate the corresponding SDCH. In the uplink, a UE reads an SCCH, and transmits an SDCH with the allocated frequency resources and format.
Because a SCCH is a channel that all UEs can receive on a shared basis, a base station performs UE IDentifier (ID)-specific Cyclic Redundancy Check (CRC) on the SCCH before transmission in order for a UE to determine whether the SCCH has been transmitted to the UE itself. Therefore, when a UE has received an SCCH from the base station, if the UE uses its own UE ID when performing CRC on the SCCH, the UE can determine if an SDCH valid to the UE itself has been scheduled.